Initial commit

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/db/migrations/002_create_training_sets.up.sql

@@ -0,0 +1,16 @@
+CREATE TABLE training_sets (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    name       TEXT NOT NULL CHECK(length(name) >= 1 AND length(name) <= 100),
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    deleted_at DATETIME
+);
+
+CREATE TABLE set_exercises (
+    set_id      INTEGER NOT NULL REFERENCES training_sets(id) ON DELETE CASCADE,
+    exercise_id INTEGER NOT NULL REFERENCES exercises(id),
+    position    INTEGER NOT NULL CHECK(position >= 0),
+    PRIMARY KEY (set_id, exercise_id)
+);
+
+CREATE INDEX idx_set_exercises_set_id ON set_exercises(set_id);